1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording for use to write data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that includes a main pole having a lower protrusion.
2. Description of the Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system in which signals are magnetized in a direction along the plane of a recording medium (the longitudinal direction) and a perpendicular magnetic recording system in which signals are magnetized in a direction perpendicular to the plane of a recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density when compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure in which a read head unit having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit having an induction-type electromagnetic transducer for writing are stacked on the top surface of a substrate. The write head unit includes a main pole for producing a write magnetic field in the direction perpendicular to the plane of the recording medium. The main pole has an end face that is located in a medium facing surface configured to face the recording medium.
The main pole includes, for example, a track width defining portion having an end located in the medium facing surface, and a wide portion connected to the other end of the track width defining portion. The track width defining portion has a top surface having a width smaller than that of the top surface of the wide portion. The width of the top surface of the track width defining portion in the medium facing surface defines the track width. To achieve higher recording densities, the track width should be as small as possible. Here, the length of the track width defining portion in the direction perpendicular to the medium facing surface will be referred to as the neck height. To improve the write characteristics of the write head unit, such as the overwrite property which indicates the overwriting capability, the neck height should be as small as possible.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically in the form of a slider. The slider has the medium facing surface. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). The slider is configured to slightly fly over the surface of the recording medium by means of an airflow that comes from the leading end into the space between the medium facing surface and the recording medium.
Here, the side of the positions closer to the leading end relative to a reference position will be defined as the leading side, and the side of the positions closer to the trailing end relative to the reference position will be defined as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
The magnetic head is typically disposed near the trailing end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs depending on the position of the magnetic head across the tracks.
In particular, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew can cause the phenomenon that signals already written on one or more tracks in the neighborhood of a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing. In the present application, this phenomenon will be called unwanted erasure. Unwanted erasure includes adjacent track erasure (ATE) and wide-area track erasure (WATE). To achieve higher recording densities, it is necessary to prevent unwanted erasure.
A known technique for preventing unwanted erasure induced by the skew is to provide a write shield having an end face that is arranged to surround the end face of the main pole in the medium facing surface, as disclosed in U.S. Pat. No. 8,427,781 B1, for example. Such a write shield will hereinafter be referred to as a wrap-around shield. The wrap-around shield includes a bottom shield located on the leading side relative to the main pole, a top shield located on the trailing side relative to the main pole, and two side shields located on opposite sides of the main pole in the track width direction. A magnetic head including the wrap-around shield is capable of preventing unwanted erasure because a magnetic flux produced from the end face of the main pole and spreading in the track width direction can be captured by the write shield.
Further improved recording densities are demanded of magnetic heads for perpendicular magnetic recording. In order for the magnetic heads including the wrap-around shield to provide improved recoding densities, it is important to achieve the following two goals. A first goal is to provide a main pole that is shaped to be small in the end face located in the medium facing surface and large in the area of a cross section parallel to the medium facing surface in the vicinity of the medium facing surface. A second goal is to reduce leakage of magnetic flux from the main pole to the wrap-around shield.
As disclosed in U.S. Pat. No. 8,427,781 B1, a main pole having a main body and a lower protrusion protruding from the main body toward the top surface of the substrate is known as one of the main poles that can achieve the aforementioned first goal. The lower protrusion is located at a distance from the medium facing surface. The lower protrusion has a front end face facing toward the medium facing surface.
A magnetic head including the wrap-around shield and the main pole having the lower protrusion suffers from a problem, as discussed below. According to a conventional method for manufacturing such a magnetic head, typically, the main pole is formed by frame plating, after the formation of the bottom shield, through the use of a mask formed by photolithography.
In this conventional manufacturing method, alignment between the lower protrusion and the two side shields depends on the position accuracy of the mask formed by photolithography. This manufacturing method suffers misalignment between the lower protrusion and the two side shields. Where a conventional magnetic head is manufactured by this manufacturing method into a structure in which the front end face of the lower protrusion is located near the medium facing surface, the occurrence of the aforementioned misalignment would bring the lower protrusion closer to one of the side shields, which would result in leakage of magnetic flux from the lower protrusion to the one of the side shields. In order to prevent the leakage of magnetic flux, conventionally, the front end face of the lower protrusion is positioned at a distance of 0.5 μm or more from the medium facing surface.
Thus, it has not conventionally been possible to achieve both of the aforementioned two goals at the same time.